Here I write about various events I was involved in and ideas that inspired me. Recently, it is more of a linux blog because I have been doing a lot of work on it. However, off and on I write on various other things that my mind just can't let go easily.

Sunday, 4 November 2012

Skype uses its own DNS

Skype is a really interesting software. Its text chat UI is mature and audio and video chat facility are very nice. Skype has this interesting ability of working independent of the DNS configuration of your system. Even when the DNS server your system is configured for, gets poisoned, Skype does not get affected.

In fact, I leverage this ability of Skype to detect network issues due to DNS service being down. On such an occasion, when the browsers were not working but Skype was, I pointed my DNS configuration to Google's DNS servers (listed below) and the browsers worked fine.

8.8.8.8
8.8.4.4

To take a deeper look, I tracked the connections Skype was making. I used the following to do that.

netstat -taucp | grep skype

Initially it was sending out packets from port 51395 of my localhost. After I logged in, I find the following connections:

H about is the hostname of my system and the IP 111.221.77.159 is owned by Microsoft, Microsoft Singapore to be specific. Interesting sequence of connections, when I lookup a contact and open the corresponding chat window.

The IPs 157.56.123.82, 91.190.216.9, 78.141.179.14 map to Microsoft Corp Redmond, Skype and Entreprise des Postes et Telecommunications respectively. After that, when I was not doing any more activity on Skype, the following network activity was seen.